The recent progress of the semiconductor manufacturing technique is outstanding, which technique is becoming more and more fine. With this tendency, there is an increasing demand for a higher degree of cleanness of the air present in a clean room as a semiconductor manufacturing site. As to suspended dust in the clean room, a target degree of cleanness is substantially attained by a facility improvement using an appropriate filter and taking the circulation of air in the clean room into account. As the material of dust proof clothes used in the clean room there is used a woven or non-woven fabric of synthetic filaments to prevent the generation of dust from the dust proof clothes. Further, as the material of dust proof clothes there also has been used fabric composed of polyester yarns and electrically conductive yarns, or a fabric subject to an antistatic finishing, to prevent dust from adhering to the dust proof clothes.
However, it has turned out that when a man works in a working space which is very strict against residual suspended dust, the worker himself or herself or the worker's undershirt is the main cause of dust generation. Thus, there exists a demand for preventing the leakage of dust generated inside the dust proof clothes to the exterior of the clothes. Although a large number of clothes called dust proof clothes have heretofore been available commercially, many of them use electrically conductive yarn as antistatic measures woven into the clothes to prevent the adhesion of dust to the clothes, or have been subjected to an antistatic finishing. In such dust proof clothes, the cuff and neck are closed with rubber or the like to prevent the leakage of dust generated from the worker's skin and undershirt through the cuff and neck. They are measures against static electricity and leakage of dust, but they are insufficient for preventing dust permeation therethrough.
For remedying the above-mentioned points, an attempt of using, for dust proof clothes, a laminate structure of woven and non-woven fabrics of filaments is described in JP60-34606A and 61-55204A.
Further, in JP60-34605A, 61-55205A and 61-75804A are described fabric-polymer laminate structures such as, for example, a synthetic filament fabric and a soft resin coated on or laminated to the surface of the fabric. Dust proof clothes of the resin laminated type are moisture-permeable because there is used a moisture-permeable waterproof resin, but the air permeability thereof is poor, so when the clothes are used over a long time, the inside of the clothes becomes stuffy, thus giving an unpleasant feeling to the person who wears the clothes. Moreover, due to a low air permeability of the fabric, there occurs the problem of dust leakage from a cuff or a neck by a pumping effect as the wearer moves. Further, because the laminated resin is inferior in abrasion resistance, the resin comes off and its performance is deteriorated after repeated wearing and washing.
The use of a multifilament yarn in the contituent filament not larger than 1.5 denier is described in JP60-259649A end JP1-321904A. Although the use of such in constituent very fine filaments is advantageous in point of improving the filtration efficiency, the use of yarns in constituent very fine filaments is not always advisable because a decrease of the constituent filament size causes deterioration of abrasion resistance or of tear strength.
Heretofore, as fabrics for dust proof clothes, both plain weave fabric and twill fabric have been used generally. Plain weave fabric is superior in abrasion resistance because there are few floating threads, but it is difficult to eliminate pores formed at intersecting portions of weaving yarns and therefore the dust filtration efficiency of plain weave fabric is inferior to that of twill fabric. As to the twill fabric, it is possible to diminish such inter-yarn pore at the point of intersection of warp yarn and weft yarn and the dust filtration efficiency thereof is generally superior to that of the plain weave fabric, but there occur a lot of floating threads, which is attributable to the weave of the twill fabric. Thus, the abrasion resistance is generally infereior to that of plain weave fabric.
Keeping the air permeability of these fabrics low is effective in preventing dust from passing through the fabrics, and high-density fabrics have so far been developed for keeping the fabric air permeability low. However, a limit is encountered in increasing the weave density of fabric, and weaving encounters a limit in diminishing the inter-yarn pore size at the point of intersection of warp yarn and weft yarn. Therefore, the fabric is subjected to shrinking in a finishing process to enhance the fabric weave density. The high-density fabric thus prepared is further subjected to calendering with use of hot pressure rolls to crush the fabric, thereby diminishing the voids present at intersecting portions of weaving yarns and enhancing the dust filtration efficiency. However, as a higher degree of cleanness in cleanroom is requested, by merely finishing a general fabric using yarns in constituent very fine filaments, it is no longer possible to meet the demand for a high dust filtering performance.
For obtaining waterproof fabrics, various attempts have been made heretofore.
According to one conventional method, a waterproof membrance is laminated to a fabric by, for example, coating or laminating to afford a waterproof composite. This method is commonly adopted and such a composite waterproof fabric is in mass production, but there remains a problem to be solved in point of comfortability because the fabric is poor in air permeability and is apt to become stuffy. There also is a problem of high cost.
According to another conventional method, waterproofness is attained without using such a waterproof membrance as is formed by coating or lamination. In this method, a high-density fabric is woven using yarns in constituent very fine filaments as at least one of warp yarn and weft yarn, which subsequent calendering with use of not pressure rolls to crush the fabric and thereby diminish pore size present at intersecting portions of weaving yarns.
Although the method just referred to above is advantageous to the improvement of waterproofness because it uses yarns in constituent very fine filaments, the use of yarns in constituents very fine filaments is not always advisable because a decrease of the constituent filament size causes deterioration of abrasion resistance or of tear strength.